Nanofiber technology has not yet developed commercially and therefore engineers and entrepreneurs have not had a source of nanofiber to incorporate into their designs. Uses for nanofibers will grow with improved prospects for cost-efficient manufacturing, and development of significant markets for nanofibers is almost certain in the next few years. The leaders in the introduction of nanofibers into useful products are already underway in the high performance filter industry. In the biomaterials area, there is a strong industrial interest in the development of structures to support living cells. The protective clothing and textile applications of nanofibers are of interest to the designers of sports wear, and to the military, since the high surface area per unit mass of nanofibers can provide a fairly comfortable garment with a useful level of protection against chemical and biological warfare agents.
Carbon nanofibers are potentially useful in reinforced composites, as supports for catalysts in high temperature reactions, heat management, reinforcement of elastomers, filters for liquids and gases, and as a component of protective clothing. Nanofibers of carbon or polymer are likely to find applications in reinforced composites, substrates for enzymes and catalysts, applying pesticides to plants, textiles with improved comfort and protection, advanced filters for aerosols or particles with nanometer scale dimensions, aerospace thermal management application, and sensors with fast response times to changes in temperature and chemical environment. Ceramic nanofibers made from polymeric intermediates are likely to be useful as catalyst supports, reinforcing fibers for use at high temperatures, and for the construction of filters for hot, reactive gases and liquids.
It is known to produce nanofibers by using electrospinning techniques. These techniques, however, have been problematic because some spinnable fluids are very viscous and require higher forces than electric fields can supply before sparking occurs, i.e., there is a dielectric breakdown in the air. Likewise, these techniques have been problematic where higher temperatures are required because high temperatures increase the conductivity of structural parts and complicate the control of high electrical fields.
It is known to use pressurized gas to create polymer fibers by using melt-blowing techniques. According to these techniques, a stream of molten polymer is extruded into a jet of gas. These polymer fibers, however, are rather large in that the fibers are typically greater than 1,000 nanometers in diameter and more typically greater than 10,000 nanofibers in diameter. U.S. Pat. No. 3,849,241 to Butin et al., discloses a melt-blowing apparatus which produces fibers having a diameter between about 0.5 microns and 5 microns.
A nozzle which uses pressurized gas to form nanofibers is known from U.S. Pat. No. 6,382,526, the disclosure of which is hereby incorporated by reference.
It is also known to combine electrospinning techniques with melt-blowing techniques. But, the combination of an electric field has not proved to be successful in producing nanofibers inasmuch as an electric field does not produce stretching forces large enough to draw the fibers because the electric fields are limited by the dielectric breakdown strength of air.
Many nozzles and similar apparatus that are used in conjunction with pressurized gas are also known in the art. For example, the art for producing small liquid droplets includes numerous spraying apparatus including those that are used for air brushes or pesticide sprayers. But, there is a need for an apparatus or nozzle capable of producing non-woven mats of nanofibers.
It is therefore an aspect of the present invention to provide a method for forming a non-woven mat of nanofibers.
It is another aspect of the present invention to provide a method for forming a non-woven mat of nanofibers, the nanofibers having a diameter less than about 3,000 nanometers.
It is a further aspect of the present invention to provide an economical and commercially viable method for forming a non-woven mat of nanofibers.
It is still another aspect of the present invention to provide an apparatus that, in conjunction with pressurized gas, produces a non-woven mat of nanofibers.
It is yet another aspect of the present invention to provide a method for forming a non-woven mat of nanofibers from fiber-forming polymers.
It is still yet another aspect of the present invention to provide a method for forming a non-woven mat of nanofibers from fiber-forming ceramic precursors.
It is still yet another aspect of the present invention to provide a method for forming a non-woven mat of nanofibers from fiber-forming carbon precursors.
It is another aspect of the present invention to provide a method for forming a non-woven mat of nanofibers by using pressurized gas.
It is yet another aspect of the present invention to provide an apparatus that, in conjunction with pressurized gas, produces a non-woven mat of nanofibers, the nanofibers having a diameter less than about 3,000 nanometers.
At least one or more of the foregoing aspects, together with the advantages thereof over the known art relating to the manufacture of non-woven mats of nanofibers, will become apparent from the specification that follows and are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a method for forming a nonwoven mat of nanofibers comprising the steps of feeding a fiber-forming material into a first slit between a first and a second member, wherein each of said first and second members have an exit end, and wherein said second member exit end protrudes from said first member exit end such that fiber-forming material exiting from said first slit forms a film on a portion of said second member which protrudes from said first member, and feeding a pressurized gas through a second slit between said first member and a third member, said second slit being located adjacent to said first slit such that pressurized gas exiting from said second slit contacts said film and ejects the fiber forming material from said exit end of said second member in the form of a plurality of strands of fiber-forming material that solidify and form a mat of nanofibers, said nanofibers having a diameter up to about 3,000 nanometers.
The present invention also includes an apparatus for forming a nonwoven mat of nanofibers by using a pressurized gas stream comprising a first member having a supply end defined by one side across the width of the first member and an opposing exit end defined by one side across the width of the first member; a second member having a supply end defined by one side across the width of the second member and an opposing exit end defined by one side across the width of the second member, the second member being located apart from and adjacent to the first member, the length of the second member extending along the length of the first member, the exit end of second member extending beyond the exit end of the first member, wherein the first and second members define a first supply slit; and a third member having a supply end defined by one side across the width of the third member and an opposing exit end defined by one side across the width of the third member, the third member being located apart from and adjacent to the first member on the opposite side of the first member from the second member, the length of the third member extending along the length of the first member, wherein the first and third members define a first gas slit, and wherein the exit ends of the first, second and third members define a gas jet space.